Quantum metrology of pump–probe spectroscopy

Pump–probe spectroscopies form an irreplaceable tool for the investigation of ultrafast dynamics and energy relaxation. The extent to which they can benefit from new quantum technologies is an open question and a very active field of research. To provide a solid theoretical foundation for this research, here we formulate the measurement of a molecular relaxation rate with a two-pulse experiment as a parameter estimation problem. We derive a quantum map for the light fields and use it to investigate possible enhancement by the use of squeezed quantum states of light and pump–probe entanglement in the impulsive limit.